The present invention is directed to a blood extraction instrument. More particularly, the present invention is directed to an improvement in the blood extraction instrument described in U.S. patent application Ser. No. 127,709, filed on Mar. 6, 1980 . More particularly, the present invention is directed to an improvement wherein the obliquely cut point of the hollow needle which is inserted into the patient's blood vessel may be readily adjusted to provide optimum insertion into the patient, and further to provide a means of insuring that the blood sample tube is retained in the instrument as desired during the procedure.
In accordance with the aforesaid U.S. patent application Ser. No. 127,709, a blood extraction instrument is provided with a hollow, cylindrical body having a closed and an open end. The open end of the cylindrical body is adapted to receive a blood sample tube. The blood sample tube is closed at the insertion end by a membrane which is retained thereon by a screw-on cap. At the closed end of the instrument, a double-ended hollow needle is mounted therein. One end, the end inside of the instrument, pierces the membrane of the blood sample tube when the blood sample tube is inserted into the hollow, cylindrical body. The other end of the double-ended hollow needle is located outside of the hollow, cylindrical body of the instrument, and is obliquely cut to provide a point which is inserted into the patient's blood vessel.
The double-ended hollow needle is eccentrically mounted on the closed end of the body of the instrument. This has been made possible by the closing of the blood sample tube by means of a screw-on cap and membrane. The eccentric location of the needle has a significant advantage in that it is possible to insert the needle into the blood vessel of the patient at a very small acute angle. In other words, it is advantageously provided that the angle that the needle makes with the blood vessel into which it is to be inserted is an acute angle, or in other words, that it is more nearly parallel to the blood vessel than perpendicular.
However, a difficulty is encountered in this technological development in that care must always be exercised to insure that outer needle point, having the obliquely cut face, be positioned with a specific orientation. The obliquely cut surface of the needle point should be turned towards the axis of the cylindrical body of the instrument, or in other words, turned away from the patient's surface of insertion. In order to insure the advantage of the eccentric location of the needle, it is necessary that the proper positioning be provided. However, from the manufacturing point of view, it is extremely difficult to insure that the thread of the portion of the needle which is screwed into the body, as well as the thread provided in the cylindrical body of the instrument are always so arranged that this particular orientation is achieved when the needle is held firmly in place. This is particularly a problem as the cylindrical body of the blood extraction instrument is used repeatedly by health care professionals, and therefore, there can be no guarantee, even if it is properly positioned when it leaves the factory, that it will continue to be properly positioned in future use.